The present invention relates to a novel, wholly aromatic polyester which can be subjected to melt-polymerization and to melt-molding and is excellent in mechanical properties.
Recently, the demand for the material excellent in rigidity, heat-resistance and resistance to chemicals and usable for preparing anything such as fibers, films and molded articles has been raised. Although polyester is broadly recognized as the material for preparing the general molded articles, polyester has not been suitable for the use requiring a high strength, because of the poor mechanical property such as flexural modulus. In order to improve the mechanical property of polyester, a method for blending a reinforcing agent such as calcium carbonate, glass fibers, etc. with polyester has been known. However, after having been blended, the density of the thus blended material becomes too large thereby to reduce the merit of the plastic material, that is, the lightness in weight, and further, in the time of molding, the abrasion, etc. of the molding machine is very severe thereby causing the practical problems.
As the polyester which does not need any reinforcing agent and is suitable for the use requiring a high strength, liquid crystalline polyester has been attracted one's attention in recent years. Since the time when W. J. Jackson published a thermally liquid crystalline high polymer comprising polyethylene terephthalate and hydroxybenzoic acid in "Journal of Polymer Science", Chemistry Edition, Vol. 14, page 2043(1976), such a specified polyester has been attracted one's attention particularly. In his publication, Jackson reported that the liquid crystalline high polymer exhibited a rigidity of more than 5 times, a strength of more than 4 times and a impact strength of more than 25 times that of polyethylene terephthalate, thereby showing the new possibility to a resin of high performances. Then, the development of liquid crystalline polyester have been continuously conducted while aiming at the coexistence of the improvement of strength and rigidity and the melt-moldability as seen in Japanese Patent Applications Laying-Open No. 53-65421, No. 54-50594, No. 55-21491, No. 55-50022 and No. 55-106220. However, in spite of the proposals of more than 100 kinds of liquid crystalline polyester, no successful polyester as the material for molded articles is offered. This is due to the large orientability of the polymer in a molten state thereof resulting in a high anisotropy of the mechanical properties.
The present inventors, as a result of their studies for relaxing the anisotropy of the mechanical properties of the liquid crystalline polyester, have attained at the present invention.